The present invention relates to a vehicular control apparatus arranged for undergoing an initial failure test after a burn-in and a method arranged therefor.
The present invention, more particularly, relates to the vehicular control apparatus having a bare-chip formed micro controller (microcomputer) mounted on a printed circuit board and arranged for undergoing the initial failure test using an external initial failure testing purpose program after the burn-in of the micro controller and the method arranged therefor before a shipment of the electronic unit which is to be mounted in a vehicle. The present invention is applicable to a combination of the vehicular control apparatus with an initial failure testing apparatus external to the vehicular control apparatus.
A Japanese Patent Application First Publication No. Heisei 7-287603 published on Oct. 31, 1995 exemplifies a previously proposed vehicular engine control apparatus arranged for undergoing an initial failure test.
In the previously proposed vehicular engine control apparatus disclosed in the above-identified Japanese Patent Application Publication, the burn-in of the microcomputers carried out and thereafter the initial failure test is carried out to detect an initial failure of the engine control unit having the micro computer before a shipment of the engine control unit, with the microcomputer of the engine control unit actually mounted on a printed circuit board and with an output voltage of a voltage stabilizer in the engine control unit boosted to a voltage higher than a normal voltage on the basis of which the engine control unit is operated in order to impose a high stress on the engine control unit at a higher temperature.
The previously proposed vehicular engine control apparatus disclosed in the above-identified Japanese Patent Application Publication has an object to undergo the burn-in and initial failure test for the vehicular engine control apparatus after a nonvolatile ROM (for example, EEP (Electrically Erasable Programmable) ROM) incorporated into the microcomputer of the engine control unit has actually mounted on the printed circuit board (on-board test). Hence, the burn-in and thereafter initial failure test for electronic parts such as a control circuit portion of the microcomputer, an input processor, an output processor, and the electronic parts except the microcomputer are carried out before they are mounted on the printed circuit board.
In the previously proposed vehicular engine control apparatus disclosed in the above-identified Japanese Patent Application Publication, controls for the individual electronic parts on the pc (printed circuit) board including the microcomputer itself have been carried out in accordance with a program stored in the nonvolatile ROM incorporated in the microcomputer.
However, an electronic control unit has recently been developed in which a bare chip formed semiconductor device mounting technique has been adopted. This bare chip mounting technique is such that a semiconductor chip of a packageless type (i.e., no package is used) is directly die bonded (die bonding method) on the pc board and, thereafter, a wire bonding method is carried out for the semiconductor chip.
It is a general practice that an inspection for the semiconductor chip is carried out when a wafer is finished or when the package is mounted on the chip. In addition, the burn-in is often carried out in order to make a screening for every vehicle applied semiconductor device before the inspection for the package to be mounted on the semiconductor chip is carried out.
It is also a general practice that in the burn-in for the semiconductor device is carried out at a higher temperature (a burn-in temperature), with a high voltage application (burn-in voltage), and for a predetermined period of time (a burn-in time duration) so as to impose a high stress on the microcomputer before the initial failure test.
The initial failure test for the electronic control unit in which the bare chip mounting technique has been adopted is carried out to examine a wire connection condition in the control unit on the pc board after the chip is mounted on the pc board and to examine electrical characteristic values such as to be determined according to the result of the initial failure test which can naturally be carried out with the semiconductor chip being actually mounted on the pc board.
In details, it is necessary to perform the initial failure test after the semiconductor chip has been mounted on the pc board.
However, when the semiconductor chip is actually mounted on the pc board in a form of the bare-chip mount, terminals (pads) of the semiconductor chip are connected to the other electronic parts on the same pc board. Hence, it is, in turn, difficult to bring a terminal (probe) of an external tester into a direct contact on an input/output terminal of the bare-chip formed microcomputer and to connect an external memory in which a testing purpose program is stored to the bare-chip formed microcomputer on the pc board in the ways as could easily be carried out in the case of the packaged microcomputer in order to confirm an operation of the bare-chip formed microcomputer.
In order to operate the microcomputer after the corresponding semiconductor chip is mounted on the pc board in the bare chip mounting form, a special-purpose program exclusively used for the initial failure test and the burn-in is needed to be stored in the nonvolatile ROM in addition to the control program usually stored in the nonvolatile ROM to be run during the normal run of the vehicle.
A quantity of the testing purpose program used for the inspection (the inspection means the (screening) test of the presence or absence of the initial failure in the microcomputer) and for the burn-in becomes tremendous so that a capacity of the nonvolatile ROM needs to be enlarged and a consequent cost of actually mounting the engine controller in the vehicle becomes accordingly high.
Furthermore, since, in the previously proposed vehicular engine control apparatus, the EEPROM is used as the nonvolatile ROM, the data written into the EEPROM is often erased so that the EEPROM lacks a reliability as the read only memory in the microcomputer.